Prosthetic heart valves are widely used for the replacement of natural valves as well as in ventricular assist devices and total artificial hearts. Valves can cause blood damage which may lead to complications such as hemolysis and thromboembolism. Hemodynamic stresses imposed on the blood elements as they pass through the valve are believed by many to play a major role in blood damage. Most studies of heart valve fluid dynamics to date have focused on the turbulent stresses generated during forward flow through the open valve. However in preliminary studies with a tilting disk valve we have found that turbulent regurgitant jets induced by regurgitant flow through the closed valve produce stresses which are an order of magnitude higher than observed in the forward flow. In addition, we have seen cavitation bubbles on the valve disk just after valve closure on every cycle. Cavitation bubbles collapse may lead to cell damage and disk wear. Therefore, studies are proposed to test the hypothesis that fluid stresses associated with regurgitant flow and cavitation (valve closure) are the dominant blood damaging mechanisms in prosthetic heart valves. In vitro investigation of valve cavitation and hemolysis will be pursued through industrial sponsorship. NIH funding is sought for the following fundamental in vitro fluid mechanical studies of regurgitant jets. 1. The instantaneous velocity field and associated (Reynolds) turbulent stresses near four different heart valve types in both the aortic and mitral position will be determined under operating conditions characteristic of natural and artificial hearts Three dimensional velocity fields, which have not been reported previously for heart valves, will be measured using laser Doppler anemometry. Particular attention will .be devoted to the regurgitant jets since the highest turbulent stresses are anticin these jets. 2. The effect of alterations in the annular gap between the valve disk and valve ring in tilting disk valves and the plane gap between the leaflets of a bileaflet valve on the turbulent stresses in regurgitant jets will be determined. Optimal gap widths, which minimize turbulent stresses without significant increases in regurgitant volume, may lead to improved hematological performance of these valves.